Polyether-based photopolymers, which are 3-(2-furyl)acrylic acid esters of phenoxy resins having a molecular weight of at least about 15,000, are known in the art (DE-OS No. 25 03 526). These photopolymers, which are used in the graphic arts, in particular for lithographic printing plates and etching resists, are produced by esterification of phenoxy resins with furyl acrylic acid derivatives. The acid chloride, i.e., furyl acryloyl chloride, is preferably used as the starting material. Because for various applications photopolymers must not contain chloride ions, which lead to premature corrosion, costly purification operations are necessary to remove the chloride ions from the esterification products. This, in turn, increases the cost of products made therefrom.
Photopolymers, i.e., photoreactive or photocrosslinkable polymers, are needed, for example, in micro-conductor technology as solder resist and insulating lacquer. Such photopolymers, however, must have a specific spectrum of properties, that is, they must be heat-resistant and capable of being processed to solder bath-resistant, fissureless films. With a single coating, they must effectively protect circuits against moisture and corrosion. Moreover, such photopolymers must be easy to prepare, manufacturered inexpensively, and capable of being processed cost-efficiently with short exposure, developing and hardening times.
Until now, epoxy resins having photo-reactive chalcone groups have been used as photopolymer-based solder resist lacquers. These solder resist lacquers are disadvantageous in that lacquer layers produced therefrom only protect against corrosion effectively if costly multiple coatings are carried out. Furthermore, because of the short-chain polymer base, several hours of thermal rehardening are required. Moreover, the production process for such solder resist lacquers is complex and hence expensive.
Therefore, it is an object of the invention to provide polyether-based photopolymers which can be produced effectively, without costly purification operations, and which are suitable for use in circuit and transmission line applications as protective and insulating layers.